Power-driven personal care devices such as electric toothbrushes or shavers are known. For example, the working implement of an electric toothbrush may include a bristle field arranged on a head that is driven by an electric motor in an oscillating rotation wherein the head may be connected to a motor shaft through a transmission train including gearing structure to transform motor shaft rotation into the desired bristle field movement. In another example, the head of a toothbrush is driven in a vibrating manner wherein the vibrating movement may be achieved by means of a rotating eccentric mass causing vibration of the brush head and the bristle field provided thereon. In still other examples, the heads of electric toothbrushes may be driven by magnetic drive systems effecting oscillating movement of the head by means of applying cyclically varying magnetic fields to a magnetic drive element.
A feature commonly found on electric toothbrushes and other personal care devices is an on/off switch or button which may be actuated to electrically activate or deactivate the driving unit of the device. The primary feature of such a switch is that it remains either in the “on” position or the “off” position until the user manually changes it. When the driving unit is activated prior to the head being placed in the mouth, the bristle field is run at predetermined speed, amplitude and/or frequency intended for operation, which may cause fluid and toothpaste to splatter around and unwanted noise to be generated.
In view of such shortcomings, it is known to provide an electric toothbrush with an automatic mode of operation in which the driving unit is activated when the toothbrush is being used in the mouth, i.e. when the bristle field is pressed against teeth or when the brush head is placed into the mouth. It is known to automatically start the driving unit of a toothbrush when contact to saliva, optionally mixed with toothpaste and water, is detected at the head which is provided with electrical conducting elements that respond to electrical conductivity of fluids present in the mouth. Furthermore, it is known to detect deflection of the toothbrush neck when pressing the head against the teeth and to activate the driving unit when such deflection exceeds beyond a certain predetermined threshold.
Such known automatic mode controls are rather complicated in structure, bulky in size and expensive in realization. The detection sensors for detecting pressure onto the bristle field or the presence of saliva need additional wiring and are detrimental to compact, small-sized designs.
Accordingly, it is desirable to provide an improved personal care device that allows for variation of the working implement speed, amplitude and/or frequency in response to load onto the working implement in a relatively simple manner.